The present invention relates to camshafts, timing gears, lifter bodies and their associated valve train mechanisms for internal combustion engines. The invention concept, incorporated in several alternative designs, is directed at improving overall volumetric efficiency of an internal combustion engine that is operated over a range of engine speeds. More particularly the invention is an improved camshaft drive, support and housing system which provides a method of adjusting, according to engine r.p.m., the distance a valve is raised from its valve seat (lift). Moreover, the invention provides a method of changing the timing and duration of valve opening and closing, relative to crankshaft and piston position, with a change in engine speed.